1. Technical Field
The present invention relates to a wavelength selective element, a manufacturing apparatus for manufacturing a wavelength selective element, a manufacturing method for manufacturing a wavelength selective element, a light source device, an image display device, and a monitor.
2. Related Art
Discharge lamps such as era-high pressure mercury lamps are generally used as light sources in projection type image display device in recent years.
However, in such a discharge lamp, there are problems in that the service lifetime is comparatively short, instantaneous lighting is difficult, the color reproducibility range is narrow, and the ultraviolet rays emitted from the lamp may degrade the liquid crystal light valve.
As an alternative to this discharge lamp, a projection type image display device using a laser light source emitting monochromatic light is proposed here.
However, while a laser light source does not have the problems mentioned above, the laser light source has the disadvantage that it has coherence.
As a result, interference fringes appear as speckle noise on the projection surface on which the laser light is projected and the image deteriorates. Thus, measures against speckle noise are necessary if highly accurate images are to be displayed.
For instance, measures against speckle noise are proposed in Published Japanese Translation No. 2004-503923 of PCT International Publication and Japanese Unexamined Patent Application, First Publication No. 2001-284718.
A light source provided with a plurality of emitters having differing central wavelengths is proposed as a device to eliminate speckle noise stated in the Published Japanese Translation No. 2004-503923 of PCT International Publication.
The bandwidth of the laser light emitted from this light source increases compared to light source with a plurality of single central wavelengths. Thus, in this manner, the speckle of the displayed image is reduced.
The external resonance type laser mentioned in Japanese Unexamined Patent Application, First Publication No. 2001-284718 is provided with a laser oscillator that oscillates laser light, and a reflective photopolymer volume hologram that reflects only the laser light of the predetermined wavelength from the laser light oscillated from the laser oscillator to the laser oscillator.
In this way, by using the volume hologram as an external resonator mirror, the width of the selected wavelength is reduced. Therefore, the coherence length of the laser light increases.
When the light is amplified by using a resonator mirror, however, problem arises in the technology mentioned in the Published Japanese Translation No. 2004-503923 of PCT International Publication since the spectral width of the laser light emitted from the light source is large and the resonator mirror has a narrow bandwidth Thus, the light emitted from the light source cannot resonate.
Also, since a volume hologram is used as the resonator mirror in the external resonance type laser mentioned in the Japanese Unexamined Patent Application, First Publication No. 2001-284718, wavelength selectivity is improved.
However, even if a light source emitting a plurality of rays of laser light is used, a single wavelength will be selected, and the speckle noise of the laser light emitted from light source including wavelength selective element cannot be suppressed.